The present invention relates to a silver halide photographic light-sensitive material, and more particularly to a silver halide photographic light-sensitive material suitable for radiographic use having a high sensitivity, wide exposure range, excellent graininess sharpness and preservability, and producing little or no fog under a safelight.
More and more complex and diverse demands have lately been made for improving the characteristics of silver halide photographic light-sensitive materials, and especially for the realization of a high-speed or ultra-high-speed silver halide photographic light-sensitive material having stable photographic characteristics. Particularly, in photographic light-sensitive materials for radiography use, in order to lessen the exposure dose of X rays against the human body, the photographic light-sensitive material is strongly desired to be so highly sensitive as to enable the obtaining of more information with less exposure dose of X rays and so improved as to produce a high-quality image with less fog.
Increasing the sensitivity of the silver halide photographic light-sensitive material (hereinafter may be called light-sensitive material) is carried out most generally by making larger the size of the silver halide contained in an emulsion layer, by the optical sensitization with use of sensitizing dyes, or the like.
It is well-known that, if the silver halide grain size is made larger, the sensitivity thereof increases. However, the light-sensitive material which uses a large-grain-size silver halide emulsion has the disadvantage that it tends to produce an increased fog or to be desensitized during the storage thereof; i.e., the preservability thereof is deteriorated, and to produce a fog due to a safelight.
A large number of prior-art techniques such as the incorporation of various additives have hitherto been disclosed for the improvement of the preservability of the silver halide photographic light-sensitive material and also for reducing the safelight fog of the photographic light-sensitive material, but it is the status quo that many of them are accompanied by undesirable secondary effects such as desensitization, and no satisfactory techniques for improving particularly the preservability of high-speed light-sensitive materials containing large-size silver halide grains have yet been obtained. In addition, such undesirable phenomena as the deterioration of the covering power with the increase in the grain size, the increase in the desensitization of the light-sensitive mateial when subjected to a mechanical pressure such as fold, and the like, also increase, so that raising the sensitivity by increasing the grain size has its limit.
Inparticular, most of the silver halide emulsions of conventional type silver halide photographic light-sensitive materials have so far used a silver halide grains having a wide grain-size distribution. Therefore, it has not always positively affirmed that an optimum chemical sensitization have been applicable to silver halide grains having every grain-size, accordingly the intrinsic sensitivity of each silver halide grain has not satisfactorily been displayed.
From the above-mentioned aspects, the techniques for making a photographic speed higher have very often been applied to silver halide photographic light-sensitive materials. The techniques of using a twin-crystal type silver halide grain are disclosed in Japanese Patent O.P.I. Publication Nos. 153428/1977, 145827/1979 and 142329/1980 and others; the techniques of using a flat-plate shaped silver halide grain are disclosed in Japanese Patent O.P.I. Publication Nos. 12792/1983, 95337/1983, 108526/1983, 111937/1983 and 113928/1983, and others; and the techniques of using a monodisperse emulsion are disclosed in Japanese Patent O.P.I. Publication Nos. 207597/1981, 178235/1982 and 49938/1983; Japanese Patent Application Nos. 53043/1983 and 54949/1983; and others. In the above-mentioned techniques, however, it has been hard to manufacture any silver halide photographic light-sensitive material which displays few fogginess and high sensitivity without affecting any other photographic characteristics.
For raising the sensitivity with the same grain size; i.e., for sensitizing methods, there are a variety of techniques. For example, a method for incorporating a development accelerator such as a thioether into an emulsion, a method for the supersensitization of a spectrally sensitized silver halide emulsion by the combined use of appropriate optical sensitizers, improved chemical sensitization techniques, and the like, have been reported. However, these methods or techniques are not necessarily applicable widely to high-speed silver halide photographic light-sensitivematerials. The silver halide emulsion to be used in a high-speed silver halide photographic light-sensitive material, since it is chemically sensitized to the utmost possible extent, when such above methods are applied, has the disadvantage that it tends to produce a fog during the storage thereof or a fog due to a safelight, or the like.
Japanese Patent Examined Publication No. 8831/1970 discloses a method of carrying out chemical sensitization by use of gold(I) mercaptide, but this method also has the disadvantage that, when the method is used alone, the stability of the light-sensitive material against heat is largely deteriorated and besides, the actual sensitivity of the light-sensitive material when exposed for a long period to a low-illuminance light is deteriorated, thereby causing the deterioration of the low-intensity reciprocity law failure characteristic.
Further, Japanese Patent Examined Publication No. 24937/1981 discloses the use of thiosuccinimide-type compounds for chemical sensitization, but this method is not enough to provide any adequate sensitization.
On the other hand, optical sensitization also is a useful sensitization means. For example, in the field of medical radiography, those conventional regular-type films sensitive to a wavelength region around 450 nm have now been replaced by orthochromatic-type photographic films orthochromatically sensitized to be further sensitive to the wavelength region range of from 540 to 550 nm. The wavelength region to which thus sensitized light-sensitive materials are sensitive is extended and at the same time the sensitivity of such materials is increased, thus allowing to reduce the exposure dose of X rays to thereby lessen its influence upon the human body. Thus, the optical sensitization is a very useful sensitization means, but there are many problems yet to be solved. For example, there are many cases where, if the combination of or the using quantities in combination of photographic emulsions, sensitizers and other additives are inappropriate, they lead to the impairment of the sensitizability or to the deterioration of the preservability of the resulting light-sensitive material, thus making it difficult to obtain adequate effects. Particularly in a high-speed light-sensitive material which uses large-size silver halide grains, the above-mentioned disadvantage tends to appear significantly, so that there is much room for further improvement.